Introduction[1]

Cultivation of medicinal and aromatic plants has had long a special rank in the traditional agricultural systems of Iran and these systems have played an important role in creating diversity and sustainability. Management of soil nutrients using organic fertilizers is among the major pillars of sustainable agriculture. Peppermint (Mentha piperita L.) is a medicinal plant, in which proper nutrition and absorption of mineral elements play an important role in increasing its quantitative and qualitative performance. The high cost of fertilizers in farming systems, soil pollution, and degradation of soil are factors that caused to full use of available renewable nutrient sources of the plant (organic and biological) with the optimal application of fertilizers in order to maintain fertility, structure, biological activity, exchange capacity and water-holding capacity of the water in the soil. The global approach to balance nutrition and the production of medicinal plants, towards the use of sustainable agricultural systems and the use of management methods, such as the application of biofertilizers, is improving the quantitative and qualitative performance of these plants. So, the use of natural inputs such as organic and biological fertilizers seems to be a good way to move towards a sustainable production system. Accordingly, due to the possible effect of organic fertilizers such as biochar and vermicompost and biological fertilizers like mycorrhizal fungi and plant growth-promoting bacteria on the quantity and quality of peppermint essential oil, this research was carried out under organic conditions.

Materials and Methods

The present research was conducted as a factorial layout based on a randomized complete block design in three replications at Sari Agricultural Sciences and Natural Resources University in 2017. The experimental site is located at 36º 39ʹ42ʺ N latitude and 53º03´54ʺ E longitude with -11 m above sea level. Soil samples were taken from depths of 0-30 cm before land preparation. Treatment consisted of biochar on two levels (0 and 10 ton ha^-1) and organic and biological fertilizers on five levels (no fertilizer, vermicompost (10 ton ha^-1), Pseudomonas fluorescens, Azotobacter and Arbuscular mycorrhizal (Glomus mosseae, G. intradices and G. etunicatum. Weeds and pests were controlled mechanically or by hand and no herbicides or pesticides were used. The measured properties also included the peppermint yield, essential oil, and essential oil compounds.

Results and Discussion

The results of the analysis of variance showed that the simple effects of biochar and organic and biological fertilizers had a significant effect on the shoot fresh weight at 1% of probability level, while the interaction effect of experimental treatments on this trait did not have a significant effect. According to the results, the application of 10 tons ha^-1 of biochar, caused a 42.96% increase in shoot fresh weight compared to no application. In the study of the simple effect of organic and biological fertilizers on shoot fresh weight, the results showed that the highest and lowest ones were obtained with mycorrhiza application and control (no application of organic and biological fertilizers) with an average of 667.95 and 418.08 g m^-2, respectively. The highest shoot dry weight with an average of 89.08 g m^-2 was associated with the combined use of biochar and mycorrhiza and the lowest one belonged to the control (no application of biochar and organic and biological fertilizers) with an average of 61.76 g m^-2. The results also showed that the interaction of biochar and organic and biological fertilizers on essential oil compounds such as Menthone, Menthol, α-Pinene, Cineol-1,8, iso Menthone, Pulegone, Piperitone oxide, Menthyl acetate, and Menthofuran was significant.

Conclusion

In general, the results showed that the use of biochar and biological and organic fertilizers can be effective in both the quality and quantity of peppermint essential oil when the highest percentage of essential oil and the most peppermint essential oil compounds were obtained in treatments with an application of biochar and biological and organic fertilizers. Where, the use of the bacterium Azobacter and Pseudomonas with biochar had the greatest effect on the quality of peppermint essential oil, especially in Menthol and Menton compounds. Finally, it can be concluded that the combined use of biochar with biological fertilizers has a significant impact on the quantitative and qualitative increase of peppermint essential oil in ecological or low-input agriculture.

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